1. Field of the Invention
The present invention relates to a double-focusing lens made of plastic for eyeglasses.
2. Prior Arts
In the prior arts, plastic-made eyeglasses are molded by a casting polymerization method by which, after a thermally-hardening type resin monomer having a catalyst added thereto is injected in a molding die and heated, the resin monomer is polymerized and hardened in the molding die.
Where a one-piece type double-focusing lens is formed, for example, the front side or rear side of a lens formed by the above-described method is polished, and two portions each having a different curvature are formed, wherein a portion of a low refractive index having a smaller curvature is made into a far-sight section, and a portion of a high refractive index having a larger curvature is made into a near-sight section.
However, since, in the above-described double-focusing lens, the curvature of the front side of the lens greatly changes at the boundary between the far-sight section and the near-sight section, and the front side of the near-side of the near-sight section further projects in comparison with the far-sight section, dust and sand, etc., are liable to be accumulated on the boundary portion at the front side of the lens, and further it is difficult to wipe off stains adhered to the boundary portion.
The present invention relates to a double-focusing lens made of plastic in view of solving the objects to improve characteristics for preventing stains and wiping off the same on the basis of the prior arts described above, in which the front and rear sides of a lens matrix having a far-sight section having a front curvature which is smaller than a rear curvature and a near-sight section having a front curvature which is larger than the front curvature of said far-sight section are coated with a matrix having a lower refractive power than a material used to form said lens matrix, and the curvatures at both the front and rear sides are formed to become uniform, whereby stains that are accumulated at a specified portion on the front and rear sides of the lens are prevented from being accumulated, and can be easily wiped off in order to solve the objects.
In summary, a double-focusing lens made of plastic according to the invention is constructed so that the front and rear sides of a lens matrix having a far-sight section having a front curvature which is smaller than a rear curvature and a near-sight section having a front curvature which is larger than the front curvature of said far-sight section are coated with a matrix having a lower refractive power than a material used to form said lens matrix, and the curvatures at both the front and rear sides are formed to become uniform. Therefore, if the curvatures of the lens are adjusted to prescribed degrees, the far sight section is able to correct myopia and the near-sight section is able to correct presbyopia. Further, there is no uneveness on the front and rear sides thereof, no stain is accumulated on any specified portions of the front and rear sides, and it is possible to easily wipe off any stains.
For example, since refraction occurs in the convergence direction only when light enters if the near-sight section of the lens matrix is made convex on the front side thereof and flat on the rear side (that is, with one side convex and the other side flat), it is necessary that the curvature of the near-sight section is increased in cases where additional power is intensified. Resultantly, the near-sight section is made thick. However, since the near-sight section is made convex at both sides so as to project to the front and rear sides of a lens matrix, a light beam transmitted through the near-sight section is refracted in a convergence direction in both cases where it enters and radiates. Accordingly, in the case of a both-side convex type, the curvature can be made smaller and the lens can be made thinner than in the case where the near-sight section is made with one side convex and the other side flat. That is, it is possible to make the thickness of a double-focusing lens thin even if a coating layer is provided on the front and rear sides of the lens matrix.
Since the molding material of the lens matrix is made of polyurethane and the coating material thereof is made of allyl diglycol carbonate resin, not only is the light transmissivity satisfactory but also the adhesivity between the lens matrix and the coating material becomes satisfactory, wherein these components can be tightly integrated. Even if the lens is subjected to external forces such as vibrations and impacts, the coating layer is not peeled off. Therefore, the present invention can bring about a double-focusing lens whose durability is excellent, wherein its practical effects are remarkable.